External Monitor Issue After macOS Sequoia 15.1.1 Update

I had this problem with my MacBook 16 inch with this upgrade. Mine would not work with usb-c to DisplayPort cables. This was fixed when I took an old usb-c to DVI cable and attached. I now have full resolution and connectivity

Well, I got my Warrky USB C to HDMI Cable and there are no problems anymore since three days.

Again 50Hz at a LG 34" wide screen monitor. The HDMI adapter plug ist a bit hot (45°C), but ok...

Thanks again to Teichfrosch

Just another data point.

I have an M1 mini with an LG 24MD4KLB-B connected via Thunderbolt and a Dell U3011 connected via HDMI, and a 15" M3 MacBook Air with another LG 24MD4KLB-B connected via Thunderbolt.

Both computers have worked perfectly with the external displays. The mini has gone from Big Sur to Sequoia without issues; the Air shipped with Sequoia.

I also have a 2019 Intel MacBook Pro with an external display connected via USB-C dock and HDMI, and it has been fine with both Ventura and Sequoia.

All three computers have 16GB of RAM.

Have this exact issue! 2018 Macbook Pro with touchscreen. I should have not updated at all!

At first when the screen started flickering I thought it was a hardware problem but it was out of nowhere and eventually the screen completely stopped working. It only works at a certain angle so I have to stick to using an external monitor but now with the latest updates even that doesn't work. My macbook won't recognize my external monitor no matter what I do. How are we supposed to work with these huge and important issues with our Macs? If Apple won't even officially refer to this issue, I will believe this is purposefully not being fixed to force users to buy new PCs! I will never buy an Apple product again ever if they don't fix this asap!

Similar problem here, my external display works fine when my MacBook Pro boots but after the computer goes to sleep/lock mode the external display stops working. By restarting the computer the problem is solved temporary but it happens every time.

Same here with Mac mini (intel & M1) with displays connected via USB-C and Sequoia 15.3.2. We're using them for digital signage and it's really a mess! I'm afraid buying the new Mac Studio and connecting 6 display will not work...

Is there any solution right now?

had the problem with my ~15yr old EIZO via DVI and Thunderbold adapter to my 2022 iMac. Tried everything, failed gloriously. Luckily enough we hadan non-used DELL display in our office that i connected via Display Port to Mini Display Port and – hallelujah! – it works!

Another vote for Apple fixing these issues.

Since upgrading to Sequoia 15.4 I started having display issues too. One of my 4k monitors (connected through a Thunderbolt 4 dock to my 14" MacBook Pro with an M1 Pro) can't be set to full resolution and is all blurry. The only workaround for now is to connect it directly to my mac, which kinda defeats the purpose of the dock.

I guess if you're lucky, the various fixes proposed here and in other forums will work for you. For me, it seems like totally a bug in the OS: I just got a refurbished Mac mini M1 from 2020 that's been erased and factory reset. It came with Sequoia 15.1.1. I didn't wait and updated straight to 15.4. Within 30 minutes, the "flickering" appeared. Same cable, same monitor that used to work (and still works) on my other Mac mini that's on Sonoma.

I just found this thread after experiencing issues with my Eizo monitor and a MacBook M3 Pro after upgrading to Sequoia 15.4. I am now at 15.4.1 and the issue persists. The external monitor screen goes black when it used to be grey. I can still use Photoshop on top of this black background, however I don't like it and it isn't helpful for colour correction which is essential to my work. If I restart my computer, the monitor screen will become grey again, though this is temporary. Furthermore, Color Navigator, the colour management software for the monitor is not making the connection anymore which is crucial to me. Are there any new fixes to try? Thx.

It worked for me. I plugged in the monitor, and in the first few seconds when the Mac detects the external display, I set it as the primary screen — and it worked. I’m using a MacBook Pro M2 (Sequoia 15.4.1) here. Not sure if that has anything to do with the issue!

This is still not fixed! I updated from 14.x to 15.5. Right after updating my external 4k monitor started going black every now an then. W T F? Apple support line played dumb, iE "not a know issue". I considering going back to linux.

I now remembered what I did to fix the issue last time this happened after a MacOS update:

Power your monitor off and turn it on again.

Hi all,

Last week I updated macOS to version 15.6 (24G84) and it seems that Apple has finally solved the issue with my monitor (Dell P2721Q).

I’ve been using it every day and the monitor hasn’t flickered yet.

It’s quite frustrating that it took more than eight months to get this issue resolved, and there’s still no RCA or any explanation for the problem, even though I had an open ticket with them through AppleCare+. Their last message to me, over two months ago, was that they didn’t know what was going on and that I would have to wait.

During this time, I tried multiple versions (including unstable ones), sent the machine to Apple for more than a week, and spent a couple of dollars on new cables and adapters.

I really hope that the issue does not appear again in a future release.

Tried this, no luck.

1. Delete /Library/Preferences/com.apple.windowserver.displays.plist file
2. Empty trash bin
3. Shut down MacBook (not a restart)